In offset lithography, a printable image is present on a printing member as a pattern of ink-accepting (oleophilic) and ink-rejecting (oleophobic) surface areas. Once applied to these areas, ink can be efficiently transferred to a recording medium in the imagewise pattern with substantial fidelity. Dry printing systems utilize printing members whose ink-repellent portions are sufficiently phobic to ink as to permit its direct application. In a wet lithographic system, the non-image areas are hydrophilic, and the necessary ink-repellency is provided by an initial application of a dampening fluid to the plate prior to inking. The dampening fluid prevents ink from adhering to the non-image areas, but does not affect the oleophilic character of the image areas. Ink applied uniformly to the printing member is transferred to the recording medium only in the imagewise pattern. Typically, the printing member first makes contact with a compliant intermediate surface called a blanket cylinder which, in turn, applies the image to the paper or other recording medium. In typical sheet-fed press systems, the recording medium is pinned to an impression cylinder, which brings it into contact with the blanket cylinder.
To circumvent the cumbersome photographic development, plate-mounting, and plate-registration operations that typify traditional printing technologies, practitioners have developed electronic alternatives that store the imagewise pattern in digital form and impress the pattern directly onto the plate. Plate-imaging devices amenable to computer control include deposition systems that apply a high-resolution pattern of image “spots” onto a carrier. The image spots have a lithographic affinity different from that of the carrier—e.g., oleophilic image spots are applied onto a hydrophilic carrier in a wet lithographic system. Inkjet deposition equipment is often used apply the image spots due to its precision, ability to eject small droplets consistent in size with commercial printing resolutions, and amenability to computer control. The inkjet fluid may interact chemically with the hydrophilic layer or, instead, may simply adhere to it. Indeed, in the latter case, the inkjet fluid may be ink that is baked into hardness following deposition.
Ink deposition systems thus avoid the need for specialized process fluids as well as environmentally detrimental chemical development. The baking step, however, may require high temperatures (130-150° C. is not uncommon) and necessitate special equipment, all of which add cost and time.